The present invention generally relates to aircraft cargo doors and, more particularly, relates to a hydraulic actuation system for use with an aircraft cargo door that employs cam-type latches and prevent opening of the aircraft cargo door even if the cargo door is not fully locked.
As is well known in the art, modern aircraft are often manufactured such that a single airframe design may be offered in a number of different configurations, such as a passenger transporting configuration, a freight transporting configuration, or a convertible configuration capable of being converted between the passenger transporting configuration and the freight transporting configuration in a relatively short period of time. To facilitate the loading and unloading of freight on these aircraft, large cargo doors are pivotally coupled to the fuselage of the aircraft to selectively reveal a body cutout or cargo opening therethrough. Typically, these cargo doors are automatically actuated between a closed position and an opened position using either a hydraulic actuation mechanism or an electromechanical actuation mechanism. Generally, electromechanical actuation mechanisms require additional space within the cargo door relative to hydraulic actuation mechanisms.
Due to the size of these cargo doors, they are often provided as outwardly opening panels, as opposed to inwardly opening, plug-type doors often used for passenger doorways. Unfortunately, there have been occurrences in commercial aviation history where outwardly opening cargo doors that were in a closed position, yet not latched or locked, have been inadvertently forced open during flight due to the aerodynamic lifting forces acting on the door. As a result of the size of the cargo door and cargo opening relative to the control surfaces of the aircraft, such inadvertent opening of the cargo door could adversely effect the ability of the flight crew to control the aircraft.
Presently, there are basically two types of outwardly opening cargo doors in service. The first type of outwardly opening cargo door employs hook-type latches to retain the cargo door in a closed position relative to the cargo opening. These hook-type latches function to simultaneously pull the cargo door into the cargo opening and latch or lock the cargo door in this closed position, such as those employed on the Boeing 737-200C, Boeing DC/MD series cargo doors, and many of the cargo doors on Airbus aircraft.
The second type of outwardly opening cargo doors employs cam-type latches to retain the cargo door in the closed position. These cam-type latches utilize a separate mechanism to first pull the door into the cargo opening before the cam-type latches latch or lock the cargo door in the closed position. Examples of this type of cargo door may be seen on the Boeing 707, 727, 747, 757, 767, and 777.
Attempts have been made to prevent the inadvertent opening of the cargo door by utilizing an electromechanical actuation mechanism in conjunction with these cam-type latches. To this end, the motor brake of the rotary motor of the electromechanically actuated mechanism serves to mechanically resist movement of the pull-in mechanism of the cam-type latch. By resisting movement of the pull-in mechanism, the cargo door is retained in a semi-closed position, even if the cargo door is not fully latched and locked. However, there are disadvantages associated with this feature. For example, as noted above, electromechanical actuation mechanism require additional space allocation within the cargo door relative to hydraulic actuation mechanisms. Many new aircraft have a reduced cargo door frame depth which will not accommodate such electromechanical actuation mechanisms. Furthermore, many existing aircraft already employ hydraulic actuation mechanisms, which would be difficult and cost-prohibitive to retrofit.
Specifically, the sequencing of the various functions to achieve closing, latching, and locking of the cargo door with a hydraulic actuation mechanism is extremely complex and increases the likelihood of hydraulic leaks developing. That is, hydraulically actuated cargo door having cam-type latches have employed a combination of priority valves, mechanically operated valves, and relief valves. The use of priority valves has been problematic in service because any change in actuation timing caused by deflection of the cargo door linkage can result in mis-sequencing and damage to the cargo door. Such cargo door linkage deflection may be caused from such things as cargo loads and/or friction in the system.
Accordingly, there exists a need in the relevant art to provide a hydraulically actuated cargo door mechanism that utilizes cam-type latches that is capable of retaining the cargo door in a semi-closed position. Furthermore, there exists a need in the relevant art to provide a hydraulically actuated cargo door mechanism that is simple in construction so as to minimize the adverse effect in actuation timing caused by the use of priority valves. Still further, there exists a need in the relevant art to provide a hydraulically actuated cargo door mechanism that overcomes the disadvantages of the prior art.
According to the principles of the present invention, a door actuation system is provided having an advantageous construction. The door actuation system is employed in an outwardly opening aircraft door for use in an aircraft having a door opening, a cam post, and a plurality of latch pins. The door actuation system includes a locking mechanism operably coupled to the door, wherein the locking mechanism is positionable in a locked position preventing the door from being opened and an unlocked position. The system further includes a pull-in mechanism that is hydraulically actuated and includes a cam slot member capable of operably engaging the cam post of the aircraft. The pull-in mechanism is positionable in an uncammed position and a cammed position. A latching mechanism is also provided that is hydraulically actuated and includes a plurality of cam latches each capable of operably receiving one of the plurality of latch pins. The latching mechanism is positionable in a latched position and an unlatched position. The pull-in mechanism and the latching mechanism are capable of preventing opening of the door when the pull-in mechanism is in the cammed position and the latching mechanism is in the latched position, even if the locking mechanism is in the unlocked position.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.